An image reading device such as a copying machine and an image scanner is widely used. In this type of image reading device, problems of deterioration in modulation transfer function (MTF), occurrence of shading, and color shift due to chromatic aberration in a central area and areas on both ends of a read image are known.
As a countermeasure, there is a method of improving an optical system such as a lens; however, a lens configuration becomes complicated and a cost increases due to an increase in the number of lenses, usage of an expensive lens and the like. Therefore, a method of not improving the optical system such as the lens but curving an image sensor side such as a linear image sensor and a semiconductor package is suggested (for example, refer to Patent Document 1).